This is a bug: Maxima output should never include bare Lisp symbols (unless
of course the user entered them), and should never include Lisp gensyms
(which cannot be input by the user). Apparently desolve uses Lisp gensyms
in the expectation that ilt/laplace will eliminate them
Of course, if Sage allowed initial "?" in symbol names, this particular
problem would go away. (Though it does seem weird that Sage is using the
stringout form of expressions rather than the s-expressions to communicate
with Maxima.)
-s
PS It would help if the actual call to Maxima were included in reports like
this, rather than the Sage form. In particular, I don't quite get the
x1=function('x1',t) construction. I reproduced the problem with
de1: diff(x1(t),t)=-3*(x2(t)^2-1);
de2: diff(x2(t),t)=1;
desolve([de1,de2],[x1(t),x2(t)]);
A simpler example:
desolve([diff(f(x),x)=f(x^2)],[f(x)]);
On Mon, Mar 14, 2011 at 17:07, Robert Dodier <robert.dodier at gmail.com>wrote:
> Short answer is that ?g1234 etc are so-called gensyms,
> that is, generated Lisp symbols.
>
> Looks like ?g1811 is a dummy variable in the Laplace transform.
> On the face of it, it looks correct, but desolve could
> pick a less confusing name.
>
> best
>
> Robert Dodier
>
> On 3/14/11, Karl-Dieter Crisman <kcrisman at gmail.com> wrote:
> > I know that sometimes in the solving code (esp. Barton's stuff) we can
> > get temporary integer or real or whatever variables that look like i3
> > or r55.
> >
> > But what the heck are the g things here? This comes from Sage ticket
> > http://trac.sagemath.org/sage_trac/ticket/9825
> >
> >
> x1(t)=ilt(-((3*laplace(x2(t)^2,t,?g1811)-x1(0))*?g1811-3)/?g1811^2,?g1811,t)
> >
> > This comes from a desolve command, but tracking down exactly what Sage
> > has sent to Maxima to get this would be tedious. Needless to say,
> > trying to search the manuals for this wasn't so helpful, e.g.
> > http://maxima.sourceforge.net/docs/manual/en/maxima_22.html has
> > examples that work, not ones that don't.
> >
> > But we'd be grateful for the help so we can properly parse Maxima
> > answers even more accurately. Thanks!
> > _______________________________________________
> > Maxima mailing list
> > Maxima at math.utexas.edu
> > http://www.math.utexas.edu/mailman/listinfo/maxima
> >
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